Reversible information display medium of liquid crystal type and non-contact IC card utilizing the same

ABSTRACT

A reversible information display medium of liquid crystal type comprises a recording layer comprising a liquid crystalline composition whose main component exhibits a glass state at room temperature and a dichroic dye, said liquid crystalline composition exhibiting an isotropic liquid state or a liquid crystal domain state by the application of heat and further exhibiting a homeotropic orientation state by the application of both heat and electric field. A non-contact IC card employing the reversible information display medium of liquid crystal type is also provided.

TECHNICAL FIELD

[0001] This invention relates to information displaying medium and moreparticularly, to reversible information displaying medium which may beused as a rewritable paper, a displaying sheet for OHP, the displayingsection of a magnetic card and the displaying section of an IC card.

BACKGROUND ART

[0002] Recently, a very large amount of paper and plastic has been usedfor displaying or recording information, which would cause variousproblems in resources and environments. Furthermore, informationrecording cards have been developed for various uses or purposes andthus information recording cards having displaying performance arerequired. The displaying section of cards and the like is preferablyrepeatedly writable and erasable so that disused information may beerased and instead necessary information are written. Moreover,displaying medium having security so that displayed information may noteasily be rewritten are required.

[0003] Displaying medium which are repeatedly writable and erasableinclude reversible thermal displaying medium comprising a high-polymermatrix and an organic low molecular compound dispersed therein so thatscattering and transmission of light may be controlled by controllingheat to be applied for display, displaying medium comprising a filmhaving a plurality of high-polymers blended together so that phaseseparation may be controlled by heat for display, reversible thermalrecording medium using a leuco pigment and a developer, and magneticrecording medium comprising micro-capsules containing dispersing agentsin solid state at normal temperature and magnetic powder dispersedtherein so that magnetic powder may be moved to the upper portion or thelower portion of the capsule by magnetic field applied under heating fordisplay.

[0004] Information displaying medium which utilize change in orientationof liquid crystal material have been proposed, which are superior to themethods mentioned above on visibility and durability. Among methodemploying low molecular liquid crystal materials there has been proposeda displaying element comprising liquid crystal/high polymer compositefilm wherein liquid crystal molecules exist in high polymer matrix.

[0005] Moreover, a system employing high-molecular liquid crystalmemorizing display and having film production performance has beenproposed. High polymer liquid crystal is one wherein molecules (mesogen)presenting the nature of liquid crystal are chemically bound to the sidechains of high molecular polymer skeleton through a flexing group,whereby settlement of liquid crystal phase is easily made at atemperature lower than glass transformation temperature Tg. JapanesePatent Application Publication Tokkai-sho 63-191673 discloses an exampleemploying such a high-molecular liquid crystal. In the reversibledisplaying medium as disclosed in the publication, scattering of lightunder liquid crystal domain state and transmission of light underisotropic liquid state are controlled by controlling heat to be appliedfor display.

[0006] Furthermore, Japanese Patent Application Publication Tokkai-sho59-10930 discloses an information recording medium which utilizeschanges in orientation when heat and electric field is applied tohigh-molecular liquid crystal or when heat is applied to high-molecularliquid crystal. Also, Japanese Patent Application Publication Tokkai-hei2-219861 discloses a method of improving a response speed by using aferroelectrics high-molecular liquid crystal. Japanese PatentApplication Publications Tokkai-hei 4-110925 and Tokkai-hei 6-265861discloses a method of improving a response speed by adding nematicliquid crystal to high-molecular liquid crystal to form smectic phase.

[0007] However, conventional systems of displaying element employingliquid crystal/high polymer composite film as mentioned above haveproblems that a large amount of high polymer material is required forformation of liquid crystal recording layer and that in case of addingdichromatic pigment or the like to be used as host-guest system,diffusion of dichromatic pigment into high polymer material deterioratescontrast.

[0008] Moreover, the method as disclosed in Tokkai-sho 63-191673 hasproblems that slow change of orientation to isotropic liquid state ormicroscopically dispersed liquid crystal domain state at a temperaturehigher than Tg of high-molecular liquid crystal necessitates annealingprocess, thereby resulting in taking a longer time for rewriting.

[0009] Moreover, the information recording medium of Tokkai-sho 59-10930has a problem that speed of orientation in simple high-molecular liquidcrystal is very low, not suitable for practical use. Also, the method ofTokkai-hei 2-219861 has problems that orientation process is requiredwhen ferroelectrics liquid crystal is used and chiral agent needs to beintroduced into high-molecular liquid crystal, thereby resulting indifficulty in synthesizing and high cost. Moreover, the methods asdisclosed in Tokkai-hei 4-110925 and Tokkai-hei 6-265861 have a problemthat smectic phase changes in orientation according to pressure, therebyresulting in deteriorating durability and conservativity or storability.

[0010] Moreover, in these methods, formation or erasing of image iseasily made by means of a single energy, thereby resulting in easytampering of the contents of display.

[0011] Under the circumstances mentioned above, there is a strong demandfor the advent of an information displaying medium having the followingfeatures: they can be used as a rewritable paper, a displaying sheet forOHP, the displaying section of a magnetic card and the displayingsection of an IC card; contrast is not deteriorated even if used for along period or repeatedly used; contrast is not deteriorated due topressure applied; and they have good conservativity, durability,visibility and resistant to tampering in use at high temperature.

[0012] Therefore, an object of this invention is to provide a reversibleinformation displaying medium having such features as mentioned aboveand a non-contact IC card utilizing such reversible informationdisplaying medium.

DISCLOSURE OF THE INVENTION

[0013] According to one aspect of the present invention, the presentreversible information display medium of liquid crystal type comprises arecording layer comprising (1) a liquid crystalline composition whosemain component exhibits a glass state at room temperature and (2) adichroic dye, the liquid crystalline composition exhibiting an isotropicliquid state or a liquid crystal domain state by the application of heatand further exhibiting a homeotropic orientation state by theapplication of both heat and electric field, the formation of letters,images and the like by the application of heat and the eliminationthereof by the application of heat and electrical field being able to becarried out, and the images being able to be retained at roomtemperature even when the application of heat and electrical field iscut.

[0014] According to one embodiment of the present invention, the presentliquid crystal composition is a high-molecular polymer liquid crystal.

[0015] According to one embodiment of the present invention, thehigh-molecular liquid crystal has a side chain represented by thefollowing general formula (1):

[0016] wherein

[0017] rings A, B, C and D independently represent an aromatic oraliphatic hydrocarbon 6 membered ring or a heterocyclic or fused ring;

[0018] Z, Z¹, Z² and Z³ independently represent a single bond, —CH₂O—,—OCH₂—, —COO—, —OCO—, —CH₂—, —CH₂CH₂—, —CH═CH—, —CF═CF— or —C≡C—;

[0019] R¹ represents a hydrogen atom, a C₁₋₈ straight or branched chainalkyl, alkoxy, alkoxyalkyl or fluoroalkyl group, a cyano group, ahalogen atom, a carboxyl group or a hydroxyl group;

[0020] X¹ and X² each independently represents a hydrogen atom, ahalogen atom or a cyano group;

[0021] l is 1 to 20;

[0022] m is 0 or 1;

[0023] n, p, q and r are independently 0 to 2; and

[0024] n+p+q+r≧1.

[0025] According to another embodiment of the present invention, thepresent liquid crystal composition is a mixture of a high-molecularliquid crystal and low-molecular liquid crystal.

[0026] According to one embodiment of the present invention, thelow-molecular liquid crystal is represented by the following generalformula (2):

[0027] wherein

[0028] Y¹ represents a hydrogen atom or a C₁₋₈ straight or branchedchain alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, alkanoyloxy oralkoxycarbonyl group;

[0029] rings E and F independently represent a benzene, cyclohexane,cyclohexene, pyrimidine or dioxane ring;

[0030] W¹ and W² independently represent a single bond, —CH₂O—, —OCH₂—,—COO—, —OCO—, —CH₂—, —CH₂CH₂—, —CH═CH— or —C≡C—;

[0031] Y represents a hydrogen or halogen atom;

[0032] Y² represents a cyano group, a halogen atom, a C₁₋₈ straight orbranched chain alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl oralkanoyloxy group or a cyano group;

[0033] Y³ represents a hydrogen atom, a halogen atom or a cyano group;and

[0034] m is 0 to 2.

[0035] According to a preferred embodiment of this invention, thecontents of said low-molecular liquid crystal in said liquid crystalcomposition is 30% by weight or below of said high-molecular liquidcrystal.

[0036] According to another embodiment of this invention, said recordinglayer is formed on an electrically conductive substrate.

[0037] According to another embodiment of this invention, saidelectrically conductive substrate is transparent and a reflecting layeror a white color layer is formed on the bottom surface of substratethrough an air layer.

[0038] According to another embodiment of this invention, said recordinglayer is formed on an electrically conductive layer formed on asubstrate.

[0039] According to another embodiment of this invention, said substrateand said electrically conductive layer are transparent and a reflectinglayer or a white color layer is formed on the bottom surface of saidsubstrate through an air layer.

[0040] According to another embodiment of this invention, saidelectrically conductive layer is transparent, an air layer is providedbetween said substrate and said electrically conductive layer, and areflecting layer or a white color layer is formed on the top surface ofsaid substrate.

[0041] According to another embodiment of this invention, an ultravioletrays absorbing layer or a protective layer is formed on said recordinglayer.

[0042] According to a preferred embodiment of the invention, fluorinesurface-active agent of 5% by weight of said liquid crystal compositionis contained in said recording layer.

[0043] According to a preferred embodiment of this invention, highpolymer resin of 20% by weight or below of said liquid crystalcomposition is contained in said recording layer.

[0044] According to a preferred embodiment of this invention, filler of20% by weight or below of said liquid crystal composition is containedin said recording layer.

[0045] According to a preferred embodiment of this invention,ultraviolet rays absorbing agent is contained in said recording layer.

[0046] According to another aspect of this invention, there is provideda non-contact IC card comprising a rewritable information displayingsection utilizing a liquid crystal type reversible informationdisplaying medium as mentioned above and an antenna section coupled toan IC tip section.

[0047] According to one embodiment of this invention, the area of theelectrically conductive layer or the metallic reflecting layer of saidinformation displaying section is equal to or smaller than 50% of thearea of said card.

[0048] According to another embodiment of this invention, theelectrically conductive layer or the metallic reflecting layer of saidinformation displaying section is divided into two or more regions, andthe area of each of said regions is equal to or smaller than 50% of thearea of said card.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments of the present invention will now be described inmore detail with reference to the accompanying drawings, in which:

[0050]FIG. 1 is a cress sectional view illustrating an exemplary modelof layered configuration of an information display medium according toone embodiment of the present invention;

[0051]FIG. 2 is a view illustrating a state in which a heat and anelectric field are applied to a recording layer according to the presentinvention so that a liquid crystal layer presents homeotropicorientation;

[0052]FIG. 3 is a view illustrating a state in which a heat is appliedto a recording layer according to the present invention until liquidcrystal phase temperature or isotropic liquid temperature for liquidcrystal high-molecule is reached, and thereafter, it is quenched so thatthe liquid crystal is randomly orientated;

[0053]FIG. 4 is a view illustrating a state in which a heat is appliedto a recording layer according to the present invention until liquidcrystal phase temperature or isotropic liquid temperature for liquidcrystal high-molecule is reached, and thereafter, it is gradually cooledso that the liquid crystal presents a domain;

[0054]FIG. 5 is a conceptual view illustrating a roller for applying anelectric field for use in erasing an image display on an informationdisplay medium according to the present invention;

[0055]FIG. 6 is a conceptual view illustrating a plate for applying anelectric field for use in erasing an image display on an informationdisplay medium according to the present invention;

[0056]FIG. 7 is a table 1 of experimental data representing arelationship between the rate of addition of low-molecular liquidcrystal and the threshold voltage;

[0057]FIG. 8 is a graph showing a change in density of colored orcolorless state with addition of a resin;

[0058]FIG. 9 is a graph showing a change in density of colored orcolorless state with addition of a filler;

[0059]FIG. 10 is a table 2 representing measurement result for densityof erased portion in sixth and seventh embodiments;

[0060]FIG. 11 is a table 3 representing measurement result forpercentage of components within compositions for use in a ninthembodiment;

[0061]FIG. 12 is a table 4 representing measurement result forpercentage of components within compositions for use in a tenthembodiment;

[0062]FIG. 13 is a table 5 representing measurement result forpercentage of components within compositions for use in a twelfthembodiment;

[0063]FIG. 14 is a schematic plan view illustrating a non-contact ICcard according to one embodiment of the present invention;

[0064]FIG. 15 is a graph representing communication distance over whichthe communication can be made as the function of changing area of aninformation display portion on the non-contact IC card in FIG. 14;

[0065]FIG. 16 is a schematic plan view illustrating a non-contact ICcard according to another embodiment of the present invention;

[0066]FIG. 17 is a schematic plan view illustrating a non-contact ICcard according to further embodiment of the present invention;

[0067]FIG. 18 is a schematic plan view illustrating a non-contact ICcard according to yet further embodiment of the present invention;

[0068]FIG. 19 is a schematic plan view illustrating a non-contact ICcard similar to that in FIG. 18, but an information display portionhaving the equal area is centrically positioned; and

[0069]FIG. 20 is a table 6 representing measurement results forcommunication distance for both non-contact IC cards in FIGS. 18 and 19.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION

[0070] Firstly, before describing various embodiments of this invention,the concept of this invention will be described. Liquid crystalcomposition as used in this invention may utilize high molecular liquidcrystal or a mixture of high-molecular liquid crystal and lowermolecular liquid crystal. The high-molecular liquid crystal is onewherein molecules (mesogen) presenting the nature of liquid crystal arechemically bound to the side chains of high-molecular skeleton through aflexing group, whereby settlement of liquid crystal phase is easily madeat a temperature lower than glass transformation temperature Tg. Sincethe viscosity of the high-molecular liquid crystal at a temperature atwhich liquid crystal phase is presented (hereinafter, referred to as aliquid crystal phase temperature) is very high, it has a very lowresponse to electric field and heat. However, it will be possible tolower the viscosity of liquid crystal phase by mixing low-molecularliquid crystal which has compatibility with high-molecular liquidcrystal in mixed condition and thus to improve the response speed. Inthis case, change in orientation due to pressure can be suppressed bypreparing the liquid crystal composition so as to present glasscondition at a room temperature.

[0071] The liquid crystal composition as used in this invention takeseither of isotropic liquid state (transparent dichromatic pigment color)and liquid crystal domain state (masking or shielding dichromaticpigment color) at a temperature lower than the liquid crystal phasetemperature. The stability between homeotropic orientation (colorless)and isotropic liquid state, liquid crystal domain state (colored) isvery high. It is stable even at a temperature higher than Tg ofhigh-molecular liquid crystal. The state of orientation may bemaintained up to a temperature in vicinity of liquid crystal phasetemperature so as to provide a good conservativity or storability ofdisplay at a high temperature. Moreover, since heat and electric fieldare required to form erased state (colorless), it has a good resistantto tampering.

[0072]FIG. 1 shows diagrammatically a cross-section of a liquid crystaltype reversible information displaying medium according to an embodimentof this invention. As shown in FIG. 1, the information displaying mediumcomprises a substrate 2, an electrically conductive layer 3, a liquidcrystal recording layer 4 and a protective layer 5.

[0073] In the present invention, as substrate 2, can be used sheethaving a stiffness sufficient for being able to be carried, for example,a sheet having a thickness of about 25 to 1000 μm, such as a polyesterfilm e.g., a polyethylene terephthalate film and a polybutyleneterephthalate film; an acrylic resin film, e.g., a polymethylmethacrylate, polymethyl acrylate and polyethylmethacrylate;furthermore, polystyrene, an acrylonitrile-butadiene-styrene copolymer,triacetic acid cellulose, polycarbonate film and polyimide films. Inaddition, usual papers such as art paper, coated paper, woodfree paper,synthetic paper; metallic foil; ceramic sheet and the like may be usedas substrate 2.

[0074] As substrate 2 having an electrical conductivity, may be used,for example, metallic foil of aluminum, chromium, nickel, cobalt,copper, silver, gold, tin, zinc, brass and stainless steel, andelectrically conductive organic materials such as carbon black, andmetal such as aluminum, chromium, nickel, cobalt, copper, silver, gold,tin, zinc, stainless steel; and oxide and nitride thereof, furthermore,electrical conductive films prepared by incorporating electricalconductive materials such as ZnOx and In—Sn—Ox into polyester films suchas polyethylene terephthalate and polybutylene terephthalate film;acrylic resin films such as polymethyl methacrylate, polymethyl acrylateand polyethylene methacrylate, furthermore a polystyrene film, anacrylonitrile-butadiene-styrene copolymer film, triacetic acid cellulosefilm, polycarbonate film, polyimide film and the like.

[0075] The electrically conductive layer 3 on the top of the substrate 2may be formed from any electrically conductive material includingelectrically conductive organic material such as carbon black; metalmaterial such as aluminum, chromium, nickel, cobalt, cupper, silver,gold, tin, zinc, bronze, stainless steal; or any oxide or nitridethereof. In addition, the electrically conductive layer 3 may be any oneof the followings: a transparent conductive layer of ZnOx, In—Sn—Ox,etc.; a vapor evaporated layer; a spattered layer; an electroless platedlayer; a thermal sprayed layer; a foil layer; or any coating layer thatmay be formed from any coating agent using a common coating procedure inwhich a powder of any of above-mentioned conductive material is producedand it is dispersed into a resin to form the coating agent. Such layeris normally deposited on the substrate 2 in the thickness of 0.01 to 50μm. In case where the vapor deposition or sputtering is used to form theconductive layer on the substrate, it is preferable that the conductivelayer is formed after depositing any anchor coat layer on the basemember in order to keep a uniform thickness for the conductive layer. Incase where the conductive layer is formed from any metal material givinga glossy surface, it also acts as the reflective layer for producinghigher contrast image. In such case, however, it may happen that thereflected component becomes stronger to narrower the angle of view fieldif there is a mirror-like surface on the conductive layer. Therefore, itis preferable that the surface of the conductive layer is roughened tosome degree. The roughness of the surface of the conductive layer may beadjusted depending on the amount of filler added to the base member, oradded to the coating liquid for the anchor coat layer on the substrate.

[0076] The conductive layer 3 may be entirely or partly formed on thesubstrate 2 of the information record medium.

[0077] In case of the transparent conductive layer 3, the color of thesubstrate 2 is visible. Therefore, when any milk white polyethyleneterephthalate film is used for the substrate 2 or it is coated with anywhite coating agent, then display of the dichromatic pigment color onthe white background is permitted. Alternatively, in case of the coloredor reflective conductive layer 3, the white coating agent may be appliedto the conductive layer 3 for permitting display of the dichromaticpigment color on the white background.

[0078] In addition, in case of using the transparent conductive layer 3,any sheet having higher transparency may be used for the substrate andany reflective or white layer may be formed on the rear surface of thesheet with intervention of an air layer therebetween, with the resultthat appearance of color of the background due to the dichromaticpigment may be reduced. Alternatively, when using the transparentconductive layer 3, an air layer may be formed between the conductivelayer 3 and the substrate 2 and any reflective or white layer may beformed on the top surface of the substrate 2 to provide the same effectas above.

[0079] The recording layer 4 used in the present invention will beexplained. in FIGS. 2, 3 and 4 respectively illustrate the phasecondition of the main components constituting the liquid crystalrecording layer. In these figures, reference 4 a represents a main chainof high-molecular liquid crystal, reference 4 b a mesogen of thehigh-molecular liquid crystal, and reference 4 c a low-molecular liquidcrystal, and reference 4 d represents dichroic dyes. The high-molecularliquid crystal usable in the present invention is that wherein themolecule (mesogen) which can function as a liquid crystal is chemicallybound to the side chains of high molecular skelton through a flexinggroup. The high-molecular liquid crystal can be changed in orientationby electric field at a liquid crystal phase temperature, can provideglassy state at a liquid crystal phase temperature and below, and canfix its liquid crystal phase. The high-molecular liquid crystal of sidechain type may be synthesized by addition polymerizing of an acrylicester, a methacrylic ester and a monomer bound to stylene throughflexing chains, or the addition reaction with vinyl substitutedmesogenic monomers to polysiloxane skeletons such as poly[oxy(methylsilylene)]. The polymerization reaction may includecopolymerization reaction. A crosslinking site or various mesogenicgroups can be introduced. While Tg or liquid crystal phase temperaturevaries depending on polymerization degree, mesogenic species, spacerlength, copolymerizing mesogenic species or its ratio. It is practicablethat Tg of high-molecular liquid crystal of side chain type is at roomtemperature or over. It is also preferred that the mesogen group ofhigh-molecular liquid crystal in the invention has electric fieldresponse, as liquid crystal phase, it may be used in either phasecondition of nematic, smectic and cholesteric phase.

[0080] Low-molecular liquid crystal 4C is used for the purpose oflowering the viscosity of the liquid crystal phase in a condition ofmixture with high molecular liquid crystal so as to improve the responsespeed.

[0081] Low-molecular liquid crystals having a good compatibility withhigh-molecular liquid crystal may be preferably used in this invention.More preferably, it has a skeleton similar to the side chain of sidechain type high-molecular liquid crystal.

[0082] Although the amount of low molecular liquid crystal to be addedis influenced by compatibility with high-molecular liquid crystal,low-molecular liquid crystal may be added in an amount so that glassstate may be formed in the mixture with high-molecular liquid crystal,preferably in an amount of 30% or below of high-molecular liquidcrystal.

[0083] Dichromatic pigments 4 d can be held by side chain molecules ofhigh-molecular liquid crystal or low-molecular liquid crystal and takethe state of orientation similar to that of the side chain molecules orlow molecular liquid crystal and perform an optical function similarlywith liquid crystal composition. Dichromatic pigment may be either ofazo or anthraquinone. It is not limited to a single component. Tone ofcolor may be adjusted by mixing of multi-components. For example, thedichromatic pigment may be M-361, SI-484, M-141, M-484, M-34, SI-497,M-403, S-409, M-412, S-428 commercially available from Mitsui Kagaku K.K., NKX-1366, G-202, G-205, G-206, G-207, G-232, G-239, G-241, G-254,G-256, G-289, G-470, G-471, G-472 commercially available from NipponKanko Shikiso K. K., KRD-201, KRD-901, KRD-902, KPD-501, KPD-906,KBD-401, KBD-701, KKD-602, KKD-604 commercially available from ShowaKakoh K. K.

[0084] The liquid crystal composition comprising a mixture ofhigh-molecular liquid crystal and low-molecular liquid crystal arehighly cohesive so as to have a low wetting. Therefore, the cohesivenessmay be lowered by adding fluorine surface-active agent to improvewetting with the electrically conductive layer. For example, thefluorine surface-active agent may be Frolard FC-430, Frolard FC-431,available from Sumitomo 3M K. K., Megafuck F-110, F-116, F-120, F-150,F-160, F-171, F-172, F-173, F-177, F-178A, F-178K, F-179, F-183, F-184,F-191, F-812, F-833 available from Dai Nippon Ink Kagaku Kogyo K. K.When an amount of fluorine surface-active agent to be added increases,paint would be frothy, thereby resulting in deteriorated adherencebetween the upper and lower layers. For this reason, the amount offluorine surface-active agent to be added may be preferably 5% by weightof liquid crystal high molecule.

[0085] The liquid crystal composition comprising high-molecular liquidcrystal or a mixture of liquid crystal high molecule and low-molecularliquid crystal has low fluidity at a temperature lower than liquidcrystal phase temperature, but has high fluidity due to lowering ofviscosity at liquid crystal phase temperature. Filler or high-molecularmaterial may be added for the purpose of suppressing this fluidity.Moreover, the adding of filler or resin is effective to provide a goodadherence between the upper and lower layers.

[0086] The filler in the present invention includes organic materials,inorganic materials, organic-inorganic copolymers or composite materialsthereof, in particularly, silica, alumina, calcium carbonate, core-shelltype particles wherein silica, alumina or calcium carbonate are coatedwith organic high molecular materials, organic-inorganic compositeparticles obtained by polycondensation of metallic alkoxides in thepresence of organic high molecular materials, polystyrene,styrene-butadiene rubber, polymethyl methacrylate, polyvinyl acetate,poly(methacrylate 2-hydroxyethyl), polyacrylamide, polyacrylic acid,poly(stylene-butylacrylate), polystylene/poly(methacrylate2-hydexyethyl)complex, poly(stylene-divinylbenzene), cellulose and thelike. Preferred refractive index of the particles varies with materialsof the primary layer. In case where metal is used as the conductivelayer, it is preferable that the refractive index of the particlesshould differ widely from the refractive index of the high-molecularliquid crystal when the surface of the layer is specular surface, and itis also preferable that the refractive index of the particles should beequivalent to the refractive index of high-molecular liquid crystal whenthe surface of the layer is roughened to make mat style. It is notpreferable that the particle size of the above fillers should be thickerthan the membrane thickness of the liquid crystal recording layerbecause of the smoothness of the membrane. The upper limit of theparticle size is 15 μm. The amount of the fillers to be added depends onits particle size. The higher amount is the lower the ratio of thehigh-molecular liquid crystal, dyes, low-molecular components and thelike. Accordingly, the contrast is made worse. Therefore, it ispreferable that the amount should be 20% by weight or below.

[0087] When the inorganic ultraviolet absorber particles are used as thefillers, the ultraviolet absorbing power may be added to the liquidcrystal layer, and the deterioration of the dichroic dyes may be reducedwhen the ultraviolet curing resin is used in the liquid crystal layer orthe intermediate layer. These inorganic ultraviolet absorber particlesinclude particles of titanium oxide, zinc oxide or cerium oxide, andcore-shell type particles wherein the surface of these particles iscoated with organic high-molecular materials. The addition of theparticles to the liquid crystal layer recording layer also has an effectto adjust ground color of the recording layer and the liquid crystalrecording layer may be made transmission type and opacity type bychanging the particle size or the mixing ratio. Preferred refractiveindex of the particles vary depending on the kinds of materials used forthe primary layer. In case where metal is used as the conductive layer,it is preferable that the refractive index of the particles shoulddiffer widely from the refractive index of the high-molecular liquidcrystal when the surface of the layer is specular surface, and it isalso preferable that the refractive index of the particles should beequivalent to the refractive index of high-molecular liquid crystal whenthe surface of the layer is roughened to make mat style. It is notpreferable that the particle size of the above fillers should be thickerthan the membrane thickness of the liquid crystal recording layerbecause of the smoothness of the membrane. The upper limit of theparticle size is 15 μm. The amount of the inorganic ultraviolet absorberparticles to be added depends on its particle size. The higher amount isthe lower the ratio of the high-molecular liquid crystal, dyes,low-molecular components and the like. Accordingly, the contrast is madeworse. Therefore, it is preferable that the amount should be 20% byweight or below.

[0088] Preferably, the materials having compatibility with thehigh-molecular liquid crystal in the monomer or oligomer condition areused in the high-molecular material to be added. It is preferable thatsuch resin material should be ultraviolet curing type. The ultravioletcuring resin includes, for example, acrylic ester and methacrylic ester;polyfunctional monomer, e.g., dipentaerythritol hexa-acrylate,trimethylolpropane triacrylate, polyethyleneglycol diacrylate,polypropyleneglycol diacrylate, polypropyleneglycol diacrylate,iscyanuric acid (ethyleneoxide modified), triacrylate, dipentaerythritoltetraacrylate, triacrylate, dipentaerythritol pentaacrylate,neopentylglycol diacrylate, hexanediol diacrylate, or polyfunctionalurethane or ester oligomers, in a monomer or oligomer state;furthermore, mono-functional monomers or oligomers, e.g., of nonylphenolmodified acrylate, N-vinyl-2-pyrrolidone,2-hydroxy-3-phenoxypropylacrylate.

[0089] The photo-polymerization initiator for curing the ultravioletcuring resin includes, for example,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenylketone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one,benzyldimethylketal, and2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropa-1-one.

[0090] The contents of high molecular material should be 20% by weightor below of high-molecular liquid crystal. When the amount ofhigh-molecular material to be added increases, phase separation betweenhigh-molecular liquid crystal and high-molecular material occurs,thereby resulting in deteriorate contrast of display. Moreover,dichromatic pigment melts into high-molecular material part, therebyresulting in further deteriorating contrast due to increase ofbackground density. For this reason, the amount of high molecularmaterial to be added is preferably 20% by weight or below.

[0091] Coating solution comprising the components as mentioned above isprepared and applied onto an electrically conductive substrate or anelectrically conductive layer to form a liquid crystal recording layer.The concentration of solid component in coating solution for the liquidcrystal recording layer is preferably 20 to 60% by weight. Forhardening, it will be necessary to set suitably various hardeningrequirements such as a kind of resin, concentration, temperature ofapplied layer, ultraviolet irradiation requirements. Suitable coating orapplying systems include a blade coating method, reverse coating method,gravure coating method, silk printing method and other methods which canperform uniform coating. The film thickness of the liquid crystalrecording layer influences resolution. The film thickness after dryingis 1 to 50 μm, preferably 3 to 10 μm so that high resolution may bemaintained and operating voltage may be low. It will be undesirable thatsmaller film thickness would provide low contrast of the informationrecording section and that larger film thickness would necessitate highoperating voltage.

[0092] The dichroic dyes added to the liquid crystal recording layer ofthe present invention may be decomposed by ultraviolet ray, to losttheir functions. Therefore, it is also possible that the ultravioletabsorbing layer may be formed onto the liquid crystal recording layer toinhibit the decomposition of the dichroic dyes. The ultravioletabsorbing layer comprises organic ultraviolet absorbers or inorganicultraviolet absorbers and high-molecular materials. The organicultraviolet absorbers or the inorganic ultraviolet absorbers are alsoused in the layer in combination. The organic ultraviolet absorber maybe selected from benzophenones, benzotriazoles, anilide oxalates,cyanoacrylates and triazines. The absorber may be either a liquid orsolid. The organic ultraviolet absorber includes, for example,2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-octoxybenzophenone, 2-hydroxy-4-dodecyloxybenzophenone,2,2′-dihydroxy-4-methoxybenzophenone,2,2′-dihydroxy-4,4′-dimethoxybenzophenone,2-hydroxy-4-methoxy-5-sulfobenzophenone,2-(2′-hydroxy-5′-methylphenyl)benzotriazole,2-(2′-hydroxy-5′-tert-butylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole,2-(2-hydroxy-3′-tert-butyl-5′-methylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-tert-butylbutylphenyl)-5-chlorobenzotriazole,2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)benzotriazole,2-{2′-hydroxy-3′-(3″,4″,5″,6″-tetrahydrophthalimidemethyl)-5′-methylphenyl}benzotriazole,and2,2-methylenebis{4-(1,1,3,3-tetramethylbutyl-6-(2H-benzotriazole-2-yl)phenol.The inorganic ultraviolet absorber particles include titanium oxide,zinc oxide, cerium oxide and core-shell type particles wherein thesurface of these particles is coated with the organic high-molecularmaterials.

[0093] There are commercially available, as organic ultravioretabsorbers, these absorbers wherein into molecule having ultravioletabsorbing power are introduced into the side chains of thehigh-molecular materials, such as Yu-daburu UV (Nihon Syokubai Inc.),PUVA (Ohtuka Kagaku K. K.) and ULS-935LH and ULS-1935LH (Ippohsya YushiKougyo K. K.). These high-molecular molecular ultraviolet absorbers ofside chain type do not cause any migration and bleeding and areexcellent in a long term use. Therefore, it is preferable that theabsorbers should be used in open-air application.

[0094] Any high-molecular materials used in the ultraviolet absorbinglayer can be used as long as they are compatible with a low-molecular orhigh-molecular ultraviolet absorber. Any inorganic ultraviolet absorbercan be used, so long as it can be dispersed. It is possible to improvethe dispersion properties by adding a dispersant.

[0095] Protective layer 5 is used to protect the liquid crystalrecording layer, and it is necessary for protective layer 5 to have ahigh fastness property. This protective layer is usually formed in athickness of about 0.5 to 10 μm by using a coating agent of mixed resincompositions comprising silicone resins, and prepolymers, oligomers,monomers and the like having polymerisable unsaturated bond or epoxygroups. The ultraviolet absorbing power may be added to the protectivelayer and the inorganic ultraviolet absorber particles may be dispersedin the protective layer.

[0096] Now description will be made to the process for creating orerasing characters or images on the information record medium. Creatingor erasing characters or images on the information record medium isperformed by application of heat or of heat and electric field.Application of heat to the information display medium may be performedby use of a heating plate, a heating roller, a thermal head, an opticalmeans and the like. Cooling speed for quenching or gradual cooling maybe controlled depending on heating temperature, heating time or acooling apparatus used.

[0097] Application of electric field to the information display mediummay be performed by use of a corona charging apparatus, a flow of ion,an electrostatic roller, an electrostatic head and the like. In casewhere the information display medium includes the conductive layer 3 onthe substrate 2 as in the above-mentioned embodiments, or the basemember 2 itself is electrically conductive, a roller for applyingelectric field as shown in FIG. 5 or a plate for applying electric fieldas shown in FIG. 6 may be used. Referring to FIG. 5 the roller forapplying electric field (hereafter referred to as “electricfield-applying roller”) consists of two electrically conductive rollersections 7 and 8 coupled together through an insulation gap 9. Whenapplying electric voltage across the roller sections 7 and 8 while theyare contact with the information display medium then the electric fieldproduced through the roller section 7 and the conductive layer 3 or theconductive substrate 2 and the roller section 8 is applied to therecording layer 4. Referring to FIG. 6 the plate for applying electricfield (hereafter referred to as “electric field-applying plate”)consists of two electrically conductive plate sections 10 and 11 coupledtogether through an insulation gap 12. When applying electric voltageacross the plate sections 10 and 11 while they are contact with theinformation display medium then the electric field produced through theplate section 10 and the conductive layer 3 or the conductive basemember 2 and the plate section 11 is applied to the recording layer 4.

[0098] Erasing of image is performed by applying heat to the informationdisplay medium, as described above, and then, applying electric field,as also described above, while the liquid crystal recording layer is atthe temperature in the range of liquid crystal phase. The liquid crystallayer presents homeotropic orientation, as shown in FIG. 2, and theliquid crystal recording layer becomes colorless. It is possible tocompletely erase the image on the information display medium by applyingheat and electric field entirely on the surface thereof. Alternativelythe image on the information display medium may partially be erased byapplying heat partially on the surface of the information displaymedium, but applying electric field entirely thereon, and vice versa.

[0099] Recording of image is performed in colorless condition by onlyapplying heat according to the process as described above. When applyingheat to the liquid crystal recording layer beyond the temperature forliquid crystal phase then the orientation of the liquid crystal becomesdisturbed so that the heat applied portion presents the dichromaticpigment color. In such case there is two kinds of orientation states forthe liquid crystal present. Firstly, if the heat is applied until someliquid crystal phase temperature or isotropic liquid temperature isreached and then it is quenched, the liquid crystal is randomlyorientated, as shown in FIG. 3, to present the dichromatic pigmentcolor. The liquid crystal recording layer in this case providestransmission characteristic. Secondly, if the heat is applied until someliquid crystal phase temperature or isotropic liquid temperature isreached and then it is gradually cooled, the liquid crystal forms adomain, as shown in FIG. 4, to present the dichromatic pigment color.The liquid crystal recording layer in this case provides shieldingcharacteristic. The information display medium that has some imagethermally recorded thereon is applied again both heat and electric fieldin order to change from the state where the liquid crystal in therecording layer is randomly oriented to the state where the liquidcrystal is aligned under electric field to enter the transparentcondition or erased condition.

[0100] According to the process as above, a colored image can be formedon a colorless background. Alternatively a colorless image may be formedon a colored background by reversibly performing the image creation anderase operations.

[0101] Accordingly the creation and erase of image can be performed atwill by repeated operations of applying heat or heat and electric field.

[0102] The concrete structure of the information displaying medium ofthis invention will be described in connection with an embodiment ofproduction.

EXAMPLE 1

[0103] Coating solution for liquid crystal recording layer is preparedby mixing 100 weight part of high-molecular liquid crystal LCP 105available from Melk Corporation and 3 weight part of dichromatic pigmentNKX-available available from Nippon Kanko Shikiso K. K. in 240 weightpart of tetrahydrofuran (THF). This coating solution is applied overpolyethylene terephthalate (PET) film having Al layer formed on the topsurface thereof by means of bar coater to form a film so that the filmthickness after drying may be 5 mm ethanol solution comprising 50 weight% of a mixture of 100 weight part of ultraviolet rays curing type resinNK-OLIGO U-6HA available form Shin Nakamura Kagaku K. K. and 5 weightpart of Irgacure 907 available from Ciba Geigy Corporation is appliedonto the film by means of bar coater to form a protective layer so thatthe film thickness of the protective layer after irradiating ultravioletrays may be 2.5 mm.

[0104] When the information recording medium is heated up to 130° C. andunder a condition of 50 Hz and 100 V heat and electric field are appliedto the information recording medium by means of an electric fieldapplying plate as shown in FIG. 6, the displaying section becomescolorless. The reflection density measured by Macbeth reflectingdensitometer is 0.6. When printing is made to the information recordingmedium by means of thermal head with energy of 0.34 mJ/dot, it takesblack color. The reflection density of the black colored portion is 1.2.Even after preserving the information displaying medium for 96 hours at80° C., there us absorbed no change in reflection density of coloredportion and colorless portion. Moreover, the information displayingmedium after preserved at high temperature is erasable and printable andthe above mentioned conditions.

EXAMPLE 2

[0105] Four types of coating solution for liquid crystal recording layerare prepared by respectively adding low-molecular liquid crystalZLI-4792, available from Merck Corporation, of 10, 20, 30 and 40% byweight of high-molecular liquid crystal to a solution comprising amixture of 100 weight part of high-molecular liquid crystal LCP105,available from Merck Corporation, and 3 weight part of dichromaticpigment NKX-1366 available from Nippon Kanko Shikiso K. K. in 240 weightpart of tetrahydrofuran (THF). Each of coating solutions is applied overpolyethylene terephthalate (PET) film having Al layer formed on the topsurface thereof by means of bar coater to form a film so that the filmthickness after drying may be 5 mm. ULS-1935 LH is applied onto the filmby means of bar coater so that the film thickness after drying may be1.5 mm. Ethanol solution comprising 50% by weight of a mixture of 100weight part of ultraviolet rays curing type resin NK-OLIGO U-6HAavailable from Shin Nakamura Kagaku K. K. and 5 weight part of Irgacene907 available from Ciba Geigy Corporation is applied onto the film bymeans of bar coater to form a protective layer so that the filmthickness of the protective layer after irradiately ultraviolet rays maybe 2.5 mm.

[0106] When the information recording medium produced in the abovementioned process is heated up to 130° C. and electric field are appliedto the information recording medium by means of an electric fieldapplying plate as shown in FIG. 6, the information recording mediumhaving low-molecular components added therein exhibit lower thresholdvoltages. The experimental results are shown in Table 1 of FIG. 7.Increase of the amount of low-molecular liquid crystal added to highmolecular liquid crystal results in lower strength of the applied film.In the information recording medium having the amount of low-molecularcomponent added larger than 20%, when it is heated up to 130° C., thereoccur wrinkles. Moreover, in the information recording medium having theamount of low-molecular liquid crystal added larger than 30%, thereoccurs phase separation between low-molecular liquid crystal andhigh-molecular liquid crystal, whereby any good applied film cannot beobtained. Judging from this results, it should be noted that the amountof low-molecular liquid crystal or low-molecular component added may bepreferably 30% by weight or below.

EXAMPLE 3

[0107] Five types of coating solution for liquid crystal recording layerare prepared by respectively adding ultraviolet rays curing type resinNK Ester A-TTM-3 available from Shin Nakamura Kagaku K. K. and aninitiator, Irgacure 907 available from Ciba Geigy Corporation (mixingrate: resin/initiator=95 weight part/5 weight part) of 10, 20, 30, 40and 50% of the total amount of high-molecular liquid crystal andlow-molecular liquid crystal to a solution comprising a mixture of 100weight part of high-molecular liquid crystal LCP 105, available fromMerck Corporation, 25 weight part of low-molecular molecular liquidcrystal ZLI-4792 available from Merck Corporation, and 3 weight part ofdichromatic pigment NKX-1366, available from Nippon Kanko Shikiso K. K.in 240 weight part of tetrahydrofuran (THF). Each of coating solutionsis applied over polyethylene terephthalate (PET) film having Al layerformed on the top surface thereof by means of bar coater to form a filmso that the film thickness after drying may be 5 mm. ULS-1935LH isapplied onto the film by means of bar coater so that the film thicknessafter drying may be 1.5 mm. Ethanol solution comprising 50% by weight ofa mixture of 100 weight part of ultraviolet rays curing type resinNK-OLIGO U-6HA available from Shin Nakamura Kagaku K. K. and 5 weightpart of Irgacure 907 available from Ciba Geigy Corporation is appliedonto the film by means of bar coater to form a protective layer so thatthe film thickness of the protective layer after irradiating ultravioletrays may be 2.5 mm.

[0108] When the information recording medium is heated up to 130° C. andunder a condition of 50 Hz and 50V heat and electric field are appliedto the information recording medium by means of an electric fieldapplying plate as shown in FIG. 6 for erasing and then printing is madeto the information recording medium by means of thermal head with energyof 0.34 mJ/dot. From these results, it has been found that in the liquidcrystal recording layer having resins of larger than 10% added thereinthere is produced no wrinkle, as produced in Example 2. However, it hasbeen found that increase of the amount of resin added leads to lowercontrast due to melting of dichromatic pigment into resin. Changes incolored density and colorless density due to adding of resin are shownin FIG. 8. Moreover, in adding of resin of larger than 20%, there occursphase separation between resin and high-molecular liquid crystal,thereby resulting in deteriorating resolution. From these results, itshould be noted that the amount of resin added to the liquid crystalrecording layer may be preferably equal to or smaller than 20%.

EXAMPLE 4

[0109] Six types of coating solution for liquid crystal recording layerare prepared by respectively adding filler, Seriguard SC-6832-Javailable from Nippon Muki Kagaku Kogyo K. K. of 5, 10, 15, 20, 25 and30% of the total amount of high-molecular liquid crystal andlow-molecular liquid crystal to a solution comprising a mixture of 100weight part of high-molecular liquid crystal LCP 105 available fromMerck Corporation, 10 weight part of low-molecular molecular liquidcrystal ZLI-4792 available from Merck Corporation and 3 weight part ofdichromatic pigment NKX-1366 available from Nippon Kanko Shikiso K. K.in 240 weight part of tetrahydrofuran (THF). Each of coating solution isapplied over polyethylene terephthalate (PET) film having Al layerformed on the top surface thereof by means of bar coater to form a filmso that the film thickness after drying may be 5 mm. ULS-1935LH isapplied onto the film by means of bar coater so that the film thicknessafter drying may be 1.5 mm. Ethanol solution comprising 50% by weight ofa mixture of 100 weight part of ultraviolet rays curing type resinNK-OLIGO U-6HA available from Shin Nakamura Kagaku K. K. and 5 weightpart of Irgacure 905 available from Ciba Geigy Corporation is appliedonto the film by means of bar coater to form a protective layer so thatthe film thickness of the protective layer after irradiating ultravioletrays may be 2.5 mm.

[0110] When the information recording medium is heated up to 130° C. andunder a condition of 50 Hz and 100V heat and electric field are appliedto the information recording medium by means of an electric fieldapplying plate as shown in FIG. 6 for erasing and then printing is madeto the information recording medium by means of thermal head with energyof 0.34 mJ/dot. From these results, it has been found that in the liquidcrystal recording layer having filler of larger than 5% added thereinthere is produced no wrinkle, as produced in Example 2. Changes incolored concentration and colorless concentration due to adding offiller are shown in FIG. 9. Increase of the amount of filler added leadsto lowering of the rate of high-molecular liquid crystal, pigment,low-molecular component, etc. in the recording layer, thereby resultingin deteriorating resolution. From these results, it should be noted thatthe amount of filler added may be preferably 20% by weight or below.

EXAMPLE 5

[0111] Eight types of coating solution for liquid crystal recordinglayer are prepared by respectively adding Frolard FC-43 available fromSumitomo 3M Corporation of 0.5, 1, 2, 3, 4, 5, 6 and 7% by weight to asolution comprising a mixture of 100 weight part of high-molecularliquid crystal LCP 105, available from Merck Corporation, 10 weight partof low-molecular liquid crystal ZLI-4792 available from MerckCorporation and 3 weight part of dichromatic pigment NKX-1366 availablefrom Nippon Kanko Shikiso K. K. in 240 weight part of tetrahydrofuran(THF). Each of coating solutions is applied over polyethyleneterephthalate (PET) film having Al layer formed on the top surfacethereof by means of bar coater to form a film so that the film thicknessafter drying may be 5 mm.

[0112] The cohesiveness of liquid crystal high molecules in the appliedliquid crystal recording layer is lowered by adding fluorinesurface-active agent, thereby resulting in improved wetness to theelectrically conductive layer. However, it has been found that adding ofthe amount of fluorine surface-active agent larger than 5% by weightleads to frothy paint and adherence between the upper and lower layersis deteriorated. From these results, it should be noted that the amountof fluorine surface-active agent to be added may be preferably 5% byweight or below of liquid crystal high molecule.

EXAMPLE 6

[0113] Coating solution for liquid crystal recording layer is preparedby mixing 100 weight part of high-molecular liquid crystal LCP 105available from Melk Corporation, 100 weight part of low-molecular liquidcrystal ZLI-4792 available from Merck Corporation, 3 weight part ofdichromatic pigment NKX-1366 available from Nippon Kanko Shikiso K. K.,12 weight part of ultraviolet rays curing type resin NK Esthel A-TMM-3available from Shin Nakamura Kagaku K. K., 0.6 weight part of Irgacure907 available from Ciba Geigy Corporation, 6 weight part of a filler,Seriguard SC-6832-J available from Nippon Muki Kagaku Kogyo K. K. and0.5 weight part of a filler, Frolard FC-430 available from Sumitomo 3MCorporation in 240 weight part of tetrahydrofuran (THF). This coatingsolution is applied over white color polyethylene terephthalate (PET)film having ITO layer formed on the top surface thereof by means of barcoater to form a film so that the film thickness after drying may be 5mm. A solution prepared by mixing 20 weight part of Seriguard SC-6832-Javailable from Nippon Muki Kagaku Kogyo K. K. in 100 weight part ofULS-1935 LH is applied onto the film by means of bar coater so that thefilm thickness after drying may be 1.5 mm. Ethanol solution comprising50% by weight of a mixture of 100 weight part of ultraviolet rays curingtype resin NK-OLIGO U-6HA available from Shin Nakamura Kagaku K. K. and5 weight part of Irgacure 907 available from Ciba Geigy Corporation isapplied onto the film by means of bar coater to form a protective layerso that the film thickness of the protective layer after irradiatingultraviolet rays may be 2.5 mm.

EXAMPLE 7

[0114] Coating solution for liquid crystal recording layer is preparedby mixing 100 weight part of high-molecular liquid crystal LCP 105available from Melk Corporation, 10 weight part of low-molecular liquidcrystal ZLI-4792 available from Merck Corporation, 3 weight part ofdichromatic pigment NKX-1366 available from Nippon Kanko Shikiso K. K.,12 weight part of ultraviolet rays curing type resin NK Ester A-TMM-3available from Shin Nakamura Kagaku K. K., 0.6 weight part of Irgacure907 available from Ciba Geigy Corporation, 6 weight part of a filler,Seriguard SC-6832-J available from Nippon Muki Kagaku Kogyo K. K. and0.5 weight part of a filler, Frolard FC-430 available from Sumitomo 3MCorporation in 240 weight part of tetrahydrofuran (THF). This coatingsolution is applied over transparent polyethylene terephthalate (PET)film having ITO layer formed on the top surface thereof by means of barcoater to form a film so that the film thickness after drying may be 5mm. A solution prepared by mixing 20 weight part of Seriguard SC-6832-Javailable from Nippon Muki Kagaku Kogyo K. K. in 100 weight part ofULS-1935 LH is applied onto the film by means of bar coater so that thefilm thickness after drying may be 1.5 mm. Ethanol solution comprising50% by weight of a mixture of 100 weight part of ultraviolet rays curingtype resin NK-OLIGO U-6HA available from Shin Nakamura Kagaku K. K. and5 weight part of Irgacure 907 available from Ciba Geigy Corporation isapplied onto the film by means of bar coater to form a protective layerso that the film thickness of the protective layer after irradiatingultraviolet rays may be 2.5 mm. Then, white color polyethyleneterephthalate film is laminated except for the center portion.

Comparison Example 1

[0115] After the information recording medium of Examples 6 and 7 areheated up to 130° C., an electric field of 50 Hz and 50V is applied tothe information recording medium by means of an electric field applyingplate as shown in FIG. 6. The density of the erased portion is measuredby Macbeth reflecting densitometer. The measurement values are shown inTable 2 of FIG. 10. The results show that the background density islowered due to introduction of air layer.

[0116] Examples of high-molecular liquid crystal which may beadvantageously used as a liquid crystal composition for the recordinglayer of the liquid crystal type reversible information displayingmedium according to this invention will be explained.

[0117] One example of the high-molecular liquid crystal has a side chainrepresented by the following general formula (1):

[0118] In the general formula (1),

[0119] rings A, B, C and D are independently an aromatic or aliphatichydrocarbon 6 membered ring, or a heterocyclic or fused ring. When theserings are a hydrocarbon 6 membered ring or a heterocyclic 6 memberedring, the examples of the rings include 1,4-phenylene,1,4-cyclohexylane, 1,4-cyclohexenylene, dioxanylene, pyridylene andpyrimidine. The examples of the fused ring include naphthylene and thelike. It is preferable that rings A, B, C and D should be a1,4-phenylene or a 1,4-cyclohexylene.

[0120] Z, Z¹, Z² and Z³ are independently a single bond, —CH₂O—, —OCH₂—,—COO—, —OCO—, —CH₂—, —CH₂CH₂—, —CH═CH—, —CF═CF— or —C≡C—. In thesegroups, it is preferable that Z, Z¹, Z² and Z³ should be —CH₂O—, —OCH₂—,—COO— or —CH₂—.

[0121] R¹ is a hydrogen atom, a C₁₋₈ straight or branched chain alkyl,alkoxy, alkoxyalkyl or fluoroalkyl group, a cyano group, a halogen atom,a carboxyl group or a hydroxyl group.

[0122] The examples of alkyl groups include methyl, ethyl, propyl,butyl, isobutyl and pentyl, and the examples of alkoxy groups includethe alkoxy groups corresponding to the above alkyl groups, the examplesof alkoxyalkyl groups include methoxymethyl, methoxyethyl, methoxypropyland ethoxymethyl, the examples of fluoroalkyl groups include fluoroalkylgroups corresponding to the above alkyl groups such as trifluoromethyland pentafluoroethyl. The halogen atom includes a fluorine, a chlorineand a bromine, and it is preferable that the halogen atom should be afluorine wherein the stability of the liquid crystal having fluorine issuperior to others.

[0123] X¹ and X² are independently a hydrogen atom, a halogen atom or acyano group. The halogen atom includes a fluorine, a chlorine and abromine, and it is preferable that the halogen atom should be a fluorinewherein the stability of the liquid crystal having fluorine is superiorto others.

[0124] When ring D is present at the end of the side chains, it ispreferable that X¹ and X² should be present at ortho positions.

[0125] l is 1 to 20, and preferably 1 to 14, and much preferably 2 to12, in view of the fact that to be added the orientation stabilitysufficient for this high-molecular liquid crystal can be provided.

[0126] One methylene group may be blocked by —CH₂O—, —OCH₂—, —COO—,—OCO— and the like groups so long as the effect of the present inventionis not adversely affected.

[0127] m is 0 or 1, and it is preferable that m should be 1.

[0128] n, p, q and r are independently 0 to 2, preferably 0 or 1. Andn+p+q+r≧1, and preferably 4≧n+p+q+r≧1, and more preferably, 4≧n+p+q+r≧2in order to improve the liquid crystal property and stiffness of thishigh-molecular liquid crystal.

[0129] This high-molecular liquid crystal may have a single side chainrepresented by the above general formula (1). This high-molecular liquidcrystal may also have 2 or more kinds of the side chains represented bythe above general formula (1) which are different from each other.

[0130] This high-molecular liquid crystal can have a side chainrepresented by the above general formula (1) as a mesogen, so that, itcan provide the reversible information display medium having theexcellent electric field response. Two or more kinds of side chainswhich are different from each represented by the above general formula(1) can be used, because the liquid crystal phase temperature and theisotopic liquid temperature can be controlled, therefore, reversibleinformation display media having the excellent storability at hightemperature can be obtained.

[0131] It is desirable that the high-molecular liquid crystal shouldhave a backbone chain obtained by addition polymerization of theunsaturated compounds. The examples of such backbone chains include apolyacrylate backbone chain, a polymethacrylate backbone chain, apolychloroacrylate backbone chain, a polyvinyl alcohol backbone chainand a polyvinyl ether backbone chain. The backbone chain of thishigh-molecular liquid crystal may comprise two or more kinds of repeatedunits which are different from each other, such as apoly(acrylate/methacrylate) backbone chain. It is preferable that thebackbone chain of the high-molecular liquid crystal should be apolyacrylate main chain or a polymethacrylate backbone chain because ofglass transition temperature (Tg) or easiness in polymerization.

[0132] It is desirable that the number average molecular weight of thehigh-molecular liquid crystal should be 2,000 or above because of themechanical strength of the recording layer of the reversible informationdisplay medium having the recording layer formed by using thishigh-molecular liquid crystal. It also is preferable that the molecularweight of this high-molecular liquid crystal should be 500,000 or lowerbecause of the solubility of the high-molecular liquid crystal in asolvent when the high-molecular liquid crystal is dissolved into thesolvent to produce the reversible information display medium compositionand because of the viscosity of the solution. It is preferable that thenumber average molecular weight of the high-molecular liquid crystalshould be 5,000 to 100,000.

[0133] This high-molecular liquid crystal can be obtained bypolymeraizing one or more kinds of monomers having the molecular siterepresented by the general formula (1), if necessary with other monomersin the range not to adversely affect the effect of the presentinvention.

[0134] The examples of monomers usable to produce the high-molecularliquid crystal include the following compounds. However, it should benotes that the monomers should not be limited to these compounds:

[0135] In this connection, a high-molecular liquid crystal can be alsoobtained by introducing a cross-linkable reaction site into ahigh-molecular liquid crystal obtained from the above compounds, andthen polymerizing with another polymerizable compound having e.g., ahydroxyl, carboxyl, mercaptan, epoxy group or amines which functionalgroup is addition polymerizable with a cross-liking agent. When therecording layer of the reversible information display medium is formedby using this high-molecular liquid crystal, the layer having athree-dimensional network can be obtained. Therefore, it is possiblethat the faster recording layer does not flow even at high temperature.

[0136] This high-molecular liquid crystal can be used singly to form therecording layer of the reversible information display medium. It isdesirable that the high-molecular liquid crystal should be used togetherthe low-molecular molecular liquid crystal which has compatibility withthe high-molecular liquid crystal in view of a response property and thelike of the recording layer to be formed.

[0137] The low-molecular compounds usable in the reversible informationdisplay medium are desirably those low molecular compounds which arecompatible with the high-molecular liquid crystal and which are stableand do not separate at a low temperature. In general, the low-molecularcompound having the similar structure to mesogen skeleton of ahigh-molecular liquid crystal has a high compatibility with thehigh-molecular liquid crystal. It is also desirable that thelow-molecular compound should reduce the viscosity in the liquid crystalphase of the high-molecular liquid crystal in view of improvement inresponse property of the recording layer to be formed. As alow-molecular compound, a single compound or 2 or more kinds ofcompounds may be used together, so that the isotopic liquid temperatureor the liquid crystal phase temperature may be controlled in a desirablerange.

[0138] It is preferable that the low-molecular compound should berepresented by the following general formula (2):

[0139] In the general formula (2), as defined above,

[0140] Y¹ is a hydrogen atom or a C₁₋₈ straight or branched chain alkyl,alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, alkanoyloxy or alkoxycarbonylgroup. Rings E and F is independently a benzene, cyclohexane,cyclohexene, pyrimidine or dioxane ring.

[0141] W¹ and W² is independently a single bond, —CH₂O—, —OCH₂—, —COO—,—OCO—, —CH₂—, —CH₂CH₂—, —CH═CH— or —C≡C—. It is preferable that W¹ andW² should be a single bond, —CH₂O—, —OCH₂—, —COO— or —C≡C—.

[0142] As defined above, Y is a hydrogen or halogen atom. Y² is a cyanogroup, a halogen atom, a C₁₋₈ straight or branched chain alkyl, alkoxy,alkenyl, alkenyloxy, alkoxyalkyl or alkanoyloxy group or a cyano group.Y³ is a hydrogen atom, a halogen atom or a cyano group.

[0143] Furthermore, m is 0 to 2, preferably 0 or 1.

[0144] The examples of the low-molecular compound usable in thecomposition include the compounds represented by the following generalformulas, however, the low-molecular compound should not be limited tothese compounds:

[0145] wherein, Y¹, Y, Y² and Y³ are as defined above.

[0146] In the compositions, it is possible that the amounts of thehigh-molecular liquid crystal and low-molecular liquid crystal to beused are properly decided depending on the kinds, the compatibilitylevel and the like of the high-molecular liquid crystal and thelow-molecular liquid crystal. In general, it is preferable the amount ofthe high-molecular liquid crystal is 99 to 60% by weight and the amountof the low-molecular liquid crystal is 1 to 40% by weight, based ontotal weight of the compositions. It is more preferable that the amountof the high-molecular liquid crystal is 95 to 70% by weight and theamount of the low-molecular liquid crystal is 5 to 30%.

[0147] Although the above mentioned embodiments have been a laminatedtype reversible information displaying medium, it will be possible toprovide a liquid crystal display in the form of a cell encapsulatinghigh-molecular liquid crystal or a composition including such liquidcrystal between electrodes. Moreover, it will be possible to performrecording and erasing of image information by light and electric fieldin a reversible information displaying medium having a light-heatconversion layer inserted into the layer structure thereof or havinginfrared rays absorbing pigment introduced into the recording layerthereof.

EXAMPLE 8

[0148] High-molecular liquid crystal (number average molecular weight9000) having a structure as expressed by the following formula I-1: ispoured into a cell having the cell thickness of 10 μm.

[0149] The ni point (isotropic liquid temperature) of thishigh-molecular liquid crystal is measured. The measurement value is 125°C. Therefore, after the cell is heated up to 125° C., an electric fieldof 50 Hz and 25V is applied to a portion of the cell. Under suchcondition, it is cooled. Then it has been found that the portion of thecell to which the electric field was applied takes homeotropicorientation state. Moreover, the cell is heated to 125° C. again andthen cooled. It has been found that the portion of the cell which tookhomeotropic orientation state takes domain state. Moreover, whileleaving the cell alone for 24 hours at 60° C., the orientation state isobserved in the term of transmittivity and through deflectingmicroscope. As a result, there has been found no change in either ofhomeotropic orientation state and domain state.

[0150] From these results, it is apparent that the high-molecular liquidcrystal is useful for a reversible information displaying mediumemploying heat and electric field.

EXAMPLE 9

[0151] Compositions a to c for reversible information displaying mediumare prepared by mixing a high-molecular liquid crystal as expressed bythe above formula I-1 and a low-molecular compound as expressed by thefollowing formula II-1 at the rates (% by mass) as shown in Table 3 ofFIG. 11.

[0152] The prepared compositions a to c are poured respectively into acell having the cell thickness of 10 μm. Their ni points and thresholdvoltages are measured. The results of measurements are shown in Table 3of FIG. 11. From the results, it is apparent that the adding oflow-molecular compound to high-molecular liquid crystal provides animproved response.

[0153] While leaving the compositions alone for 48 hours at roomtemperature, the stability of phase observed. While in the composition Cthere occurs phase separation, the compositions a and b are stable. Forthe compositions a and b left alone for 24 hours at 60° C. withhomeotropic orientation state and liquid crystal domain state, there hasbeen found no change in orientation states as observed in the term oftransmittivity and by deflecting microscope.

[0154] From these results, it is apparent that adding of low-molecularcompound to high-molecular liquid crystal provides an improved responsespeed while maintaining a good conservativity or storability.

EXAMPLE 10

[0155] Compositions are prepared by adding dichromatic pigment NKX-1366available from Nippon Kanko Shikiso K. K. to high-molecular liquidcrystal I-1 as used in Example 8 and the compositions a and b asprepared in Example 2 at a rate of 1% of the total mass of thecomposition. The prepared compositions are poured into a cell having thecell thickness of 10 μm. The homeotropic orientation as formed byapplication of heat and electric field and transmittivity of isotropicliquid state as formed by heating up to ni point are measured. Themeasurement of transmittivity is performed by use of light having awavelength of 670 mm.

[0156] For comparison, compositions are prepared by adding dichromaticpigment to low-molecular liquid crystal (ZLI-4792 available from MelkCorporation) as mentioned above. For the compositions, similarmeasurement is made. The results of measurement are shown in Table 4 ofFIG. 12.

[0157] From these results, it is apparent that the transmittivity inhomeotropic orientation of either of the mixtures is similar andhigh-molecular liquid crystal and low-molecular liquid crystal takesimilar orientation states. Moreover, for the transmittivity inisotropic liquid state, the transmittivity of high-molecular liquidcrystal is lower than that of low-molecular molecular liquid crystal.This is because the high-molecular liquid crystal forms liquid crystaldomain structure which causes diffusion deflecting.

EXAMPLE 11

[0158] Coating solution for the recording layer of reversing informationdisplaying medium is prepared by mixing 100 weight part of thecomposition a as prepared in Example 9 and 3 weight part of dichromaticpigment NKX-1366 available from Nippon Kanko Shikiso K. K. in 240 weightpart of tetrahydrofuran (THF). This coating solution is applied overpolyethylene terephthalate (PET) film having Al layer formed on the topsurface thereof by means of bar coater to form a film so that the filmthickness after drying may be 5 μm. Then, ethanol solution comprising50% by mass of a mixture of 100 weight part of ultraviolet rays curingtype resin NK-OLIGO U-6HA available from Shin Nakamura Kagaku K. K. and5 weight part of cross-linking agent Irgacure 907 available from CibaGeigy Corporation is prepared. This solution is applied onto therecording layer by means of bar coater to form a protective layer sothat the film thickness of the protective layer after drying may be 2.5μm.

[0159] When the produced reversible information displaying medium isheated up to 130° C. and under a condition of 50 Hz and 50V head andelectric field are applied to the information displaying medium by meansof electrodes as shown in FIG. 6, the displaying section becomescolorless. The reflection density of the displaying section measured byMacbeth reflecting densitometer is 0.6. When printing is made to thedisplaying section of the reversible information displaying medium bymeans of thermal head with energy of 0.34 mJ/dot, the printed sectiontakes black color. The reflection density of the printed sectionmeasured is 1.2. Even after preserving the reversible informationdisplaying medium for 96 hours at 80° C., there is observed no change inreflection density of printed section and not printed section of thedisplaying section. Moreover, heat and electric field are applied to thedisplaying section of the reversible information displaying mediumpreserved at high temperature to erase the printed section. Nodifference in reflection density between the erased section and the notinitially printed section is recognized.

EXAMPLE 12

[0160] Compositions d to f are reversible recording medium are preparedby mixing a high-molecular liquid crystal having a structure asexpressed by the following formula I-2 (a polymer of 90% by mol of amonomer corresponding to repetition unit having side chain A and 10% bymol of a monomer corresponding to repetition unit having side chain B:number average molecular weight 12,000) and a low molecular compound asexpressed by the following formula II-2 or the following formula II-3 atthe rates (% by mass) as shown in Table 5 of FIG. 13.

[0161] Three types of coating solutions for the recording layer ofreversible information displaying medium are prepared by mixing 100weight part of the respective composition and 3 weight part ofdichromatic pigment NKX-1366 available from Nippon Kanko Shikiso K. K.in 240 weight part of tetrahydrofuran (THF). Each of the preparedcoating solution is applied over polyethylene terephthalate (PET) filmhaving Al layer formed on the top surface thereof by means of bar coaterto form a film so that the film thickness after drying may be 5 μm.Then, ethanol solution comprising 50% by mass of a mixture of 100 weightpart of ultraviolet rays curing type resin NK-OLIGO U-6HA available fromShin Nakamura Kagaku K. K. and 5 weight part of cross-linking agentIrgacure 907 available from Ciba Geigy Corporation is prepared. Thissolution is applied onto the recording layer by means of bar coater toform a protective layer so that the film thickness of the protectivelayer after drying may be 2.5 μm.

[0162] The reversible information display medium thus produced was thenheated to the temperature of 130° C. and was applied a thermal electricfield at 50V, 50 Hz by use of the electrode as shown in FIG. 6. As theresult, a colorless display portion was formed. The reflection densityof the display portion was at 0.6 that was measured with a Macbethreflection density meter. Printing was performed on the display portionof the reversible information display medium by the thermal head at theenergy of 0.34 mJ/dot so that the printed portion was colored black. Thereflection density of the printed portion was measured at 1.2. Afterkeeping the reversible information display medium at 90° C. for theperiod of 96 hours, change in reflection density with the time wasobserved for the printed portion and the remaining portion in thedisplay portion that was not yet printed. Then there was no change inreflection density observed in either of the portions. Next, thereversible information display medium kept at higher temperature wasapplied a thermal electric field for the purpose of erasing. There is nodifference in reflection density observed between the erased portion andthe portion that has not initially been printed.

[0163] Now, description will be made to an embodiment in which theliquid crystal type reversible information display medium as describedabove is used for an information display portion of a non-contact ICcard.

[0164] Recently, great attention has been paid to a non-contact IC cardthat is effectively used for an information recording card in view ofthe resource problem, environmental problem and security problem. Unlikea magnetic recording card, the non-contact IC card is capable oftransmitting information via an antenna. Therefore, if it is applied toa commutation ticket for a train, the time required for a person to passthrough an automatic ticket examiner machine can be shortened.

[0165] Such IC card is required to have a display portion formed thereonfor displaying and transmitting visual information including internalinformation and messages. Unlike a magnetic recording card, the IC cardis required to provide higher possibility of reuse and repeated use overlonger period of time, and the display portion thereon is required tohave durability and preservation characteristic for repeated use. Inaddition, resistant to tampering characteristic is required. Therefore,the liquid crystal type reversible information display medium accordingto the present invention as described above can advantageously be usedfor the information display portion of such kind of the non-contact ICcard.

[0166] However, as described above, the liquid crystal type reversibleinformation display medium according to the present invention includesan electrically conductive layer and a reflective metal layer, andtherefore, if it is used for the display portion of the non-contact ICcard, the following problems should be solved. First of all, when thenon-contact IC card communicates with a read/write unit, any capacitiveeffect may be caused due to electrostatic capacity between theconductive layer or reflective layer, and the shield layer, antenna andIC chips on the IC card. Therefore, the communication with the externalunit may be interfered. In addition, when the non-contact IC cardcommunicates with a read/write unit, an eddy current may flow in theconductive layer or the reflective metal layer due to magnetic fieldproduced by an electromagnetic wave sent by the read/write unit to thenon-contact IC card. The eddy current may induce magnetic field thatcauses canceling of the electromagnetic wave sent by the read/write unitto the non-contact IC card, with the result that the communication maybe interfered.

[0167]FIG. 14 is a schematic plan view illustrating a non-contact ICcard in which an area of a rewritable information display portion usingthe liquid crystal type reversible information display medium accordingto the present invention is less than 50% of the entire card area inorder to solve the above-mentioned problems as much as possible. Asshown in FIG. 14, the non-contact IC card 10 includes an IC chip 12 andan antenna 13 buried in a base member 11 as well as an informationdisplay portion 40 including an electrically conductive metal reflectionlayer formed on the surface of the base member 11. According to thisembodiment the information display portion 40 is provided substantiallyin a left-hand half portion of the base member 11 and positioned awayfrom the antenna 13.

[0168]FIG. 15 is a graph representing the measurement result for thecommunication distance over which the communication can be made betweenthe non-contact IC card of FIG. 14 and the read/write unit as an areathat the information display portion 40 occupies is changed, in otherwords, an area of the conductive metal reflection layer (including theinformation display portion) is changed relative to that of the IC card.In this graph the communication distance represents the relative value,assuming that the communication distance with no metal reflective layeris at 100%. It can be seen in the graph of FIG. 15 that if the area ofthe metal reflective layer is not greater than 50% of the IC card areathen the communication distance of not less than 90% can be assured ascompared to the case of no metal reflection layer present.

[0169]FIG. 16 is a schematic plan view illustrating another embodimentof a non-contact IC card according to the present invention. In thisembodiment an information display portion including an electricallyconductive layer and a metal reflection layer is divided into pluralsections so that the total information display area of 40A+40B is keptat the value not greater than 50% of the IC card area. In the example ofFIG. 16 the information display portion is divided into two sections,but the present invention is not limited to such number. Therefore, theinformation display portion can be divided into any number of sections.

[0170] In addition, in such case where the information display portionis divided into plural sections as described above, each of theconductive layers and the metal reflection layers in each of the dividedinformation display sections may not necessarily be electricallyinsulated. Accordingly the information display sections 40A and 40B maybe connected to each other via a connection 41 at center portion of theIC card, as shown in FIG. 17.

[0171] By dividing the conductive display portion in such manner, theeddy current that may interfere the communication will be induced ineach of the sections, with the result that the eddy current thatcirculates around the periphery of the card and adversely affects can beeliminated.

[0172]FIG. 18 is a schematic plan view illustrating further embodimentof a non-contact IC card according to the present invention. In thisembodiment an information display portion 40C including an electricallyconductive layer and a metal reflection layer is formed at either oneside of a centerline 6 passing in parallel to the short sides of an ICcard 10. In such configuration an eddy current circulating in the centerportion of the card can be eliminated.

[0173]FIG. 19 is a schematic plan view illustrating yet furtherembodiment of a non-contact IC card in which an electrically conductiveinformation display portion 40D having the same area as that of theinformation display portion 40C in FIG. 18 is positioned at the centerof the IC card 10. FIG. 20 is a table 6 representing measurement resultsfor the communication distance for both non-contact IC cards in FIGS. 18and 19. As can be seen in the table of FIG. 20 it is advantageous thatthe conductive information display portion is positioned away from thecenter portion of the card in order to effectively reduce anyelectromagnetic wave shielding effect, even if the area of theconductive information display portion is kept constant.

[0174] It is more preferable that the conductive information displayportion 40 is positioned so as not to overlap with the antenna 13 andthe IC chip 12, as in the embodiment of FIG. 14. Because suchconfiguration effectively prevents any interfering from occurring due tothe electrostatic coupling between the conductive sections, the antennaand the IC chip to provide a stable communication. Furthermore, the ICchip may some times have a convex surface, which is defective in thatits contact with the energy supplying apparatus such as the thermalhead, heating roller and electric field applying unit becomes poor uponerasing the characters, thereby leading to any unevenly erased portion.In order to avoid such defect it is preferable to position theinformation display portion away from the IC chip.

[0175] Industrial Applicability

[0176] It is apparent from the foregoing that a liquid crystal typereversible information display medium according to the present inventioncan perform a recording operation with heating and an erasing operationwith heating and application of electric field so that older informationcan be erased while keeping only necessary information. In addition, ithas fast response, good conservation at higher and lower temperature,resistant to light, higher durability, good visual perceiving, andresistant to tampering characteristics. Accordingly it can effectivelybe used for a display portion of a recording medium for long-term use,such as a magnetic card, an IC card, etc.

[0177] A non-contact IC card including a rewritable information displayportion according to the present invention can erase any unnecessaryinformation and can display the necessary information without anyadverse effect to the IC card characteristics. Therefore, it isextremely effective for use with a commutation ticket for a train and anentry ticket.

1. A reversible information display medium of liquid crystal typecomprising a recording layer comprising a liquid crystalline compositionwhose main component exhibits a glass state at room temperature and adichroic dye, said liquid crystalline composition exhibiting anisotropic liquid state or a liquid crystal domain state by theapplication of heat and further exhibiting a homeotropic orientationstate by the application of both heat and electric field.
 2. Thereversible information display medium of liquid crystal type accordingto claim 1, wherein said liquid crystal composition is a high-molecularpolymer liquid crystal.
 3. The reversible information display medium ofliquid crystal type according to claim 2, wherein said high-molecularliquid crystal has a side chain represented by the following generalformula (1):

wherein rings A, B, C and D independently represent an aromatic oraliphatic hydrocarbon 6 membered ring, or a heterocyclic or fused ring;Z, Z¹, Z² and Z³ independently represent a single bond, —CH₂O—, —OCH₂—,—COO—, —OCO—, —CH₂—, —CH₂CH₂—, —CH═CH—, —CF═CF— or —C≡—C—; R¹ representsa hydrogen atom, a C₁₋₈ straight or branched chain alkyl, alkoxy,alkoxyalkyl or fluoroalkyl group, a cyano group, a halogen atom, acarboxyl group or a hydroxyl group; X¹ and X² each independentlyrepresents a hydrogen atom, a halogen atom or a cyano group; l is 1 to20; m is 0 or 1; n, p, q and r are independently 0 to 2; and n+p+q+r≧1.4. The reversible information display medium of liquid crystal typeaccording to claim 1, liquid crystal composition is a mixture of ahigh-molecular liquid crystal and low-molecular liquid crystal.
 5. Thereversible information display medium of liquid crystal type accordingto claim 4, wherein said low-molecular liquid crystal is represented bythe following general formula (2):

wherein Y¹ represents a hydrogen atom or a C₁₋₈ straight or branchedchain alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, alkanoyloxy oralkoxycarbonyl group; rings E and F independently represent a benzene,cyclohexane, cyclohexene, pyrimidine or dioxane ring; W¹ and W²independently represent a single bond, —CH₂O—, —OCH₂—, —COO—, —OCO—,—CH₂—, —CH₂CH₂—, —CH═CH— or —C≡C—; Y represents a hydrogen or halogenatom; Y² represents a cyano group, a halogen atom, a C₁₋₈ straight orbranch chained alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl oralkanoyloxy group or a cyano group; Y³ represents a hydrogen atom, ahalogen atom or a cyano group; and m is 0 to
 2. 6. The reversibleinformation display medium of liquid crystal type according to claim 4,wherein the contents of said low-molecular liquid crystal in said liquidcrystal composition is 30% by weight or below of said high-molecularliquid crystal.
 7. The reversible information display medium of liquidcrystal type according to claim 1, wherein said recording layer isformed on an electrically conductive substrate.
 8. The reversibleinformation display medium of liquid crystal type according to claim 7,wherein said electrically conductive substrate is transparent and areflecting layer or a white color layer is formed on the bottom surfaceof substrate through an air layer.
 9. The reversible information displaymedium of liquid crystal type according to claim 1, wherein saidrecording layer is formed on an electrically conductive layer formed ona substrate.
 10. The reversible information display medium of liquidcrystal type according to claim 9, wherein said substrate and saidelectrically conductive layer are transparent and a reflecting layer ora white color layer is formed on the bottom surface of said substratethrough an air layer.
 11. The reversible information display medium ofliquid crystal type according to claim 9, wherein said electricallyconductive layer is transparent, an air layer is provided between saidsubstrate and said electrically conductive layer, and a reflecting layeror a white color layer is formed on the top surface of said substrate.12. The reversible information display medium of liquid crystal typeaccording to claim 1, wherein an ultraviolet rays absorbing layer or aprotective layer is formed on said recording layer.
 13. The reversibleinformation display medium of liquid crystal type according to claim 1,wherein fluorine surface-active agent of 5% by weight of said liquidcrystal composition is contained in said recording layer.
 14. Thereversible information display medium of liquid crystal type accordingto claim 1, wherein high polymer resin of 20% by weight or below of saidliquid crystal composition is contained in said recording layer.
 15. Thereversible information display medium of liquid crystal type accordingto claim 1, wherein filler of 20% by weight or below of said liquidcrystal composition is contained in said recording layer.
 16. Thereversible information display medium of liquid crystal type accordingto claim 1, wherein ultraviolet rays absorbing agent is contained insaid recording layer.
 17. A non-contact IC card comprising a rewritableinformation displaying section utilizing a liquid crystal typereversible information displaying medium as defined in any one of claims1 to 16 and an antenna section coupled to an IC tip section.
 18. Thenon-contact IC card according to claim 17, wherein the area of theelectrically conductive layer or the metallic reflecting layer of saidinformation displaying section is equal to or smaller than 50% of thearea of said card.
 19. The non-contact IC card according to claim 17,wherein the electrically conductive layer or the metallic reflectinglayer of said information displaying section is divided into two or moreregions, and the area of each of said regions is equal to or smallerthan 50% of the area of said card.